Water-soluble polymers containing 2-acrylamido-2-methylpropane-sulfonic acid, sodium salt (AMPS)-acrylamide-N,N-diallylacetamide

ABSTRACT

Novel water-soluble terpolymers comprising: -Ingredients Mole % -2-acrylamido-2-methylpropane- 57-61 -sulfonic acid, sodium salt (AMPS) -acrylamide 20-35 -N,N-diallylacetamide  4-23 -  These terpolymers provide high temperature fluid loss additives and rheology stabilizers for high calcium-containing brine clay drilling fluids.

This application is a divisional application of our copendingapplication, Ser. No. 530,814, filed Sept. 9, 1983, which is now U.S.Pat. No. 4,502,966.

INTRODUCTION

A serious problem is encountered when clay-based oil well drillingfluids are subjected to conditions of high temperature and high pressurein conjunction with utilization of high calcium-containing brines whichare used to prepare these drilling fluids. When these conditions exist,conventional drilling fluid polymeric additives such as acrylamidepolymers, when used as stabilizers for these fluids, tend to be renderedineffective.

Recently a partial solution to the problem has been provided by theutilization as a fluid loss additive and rheology stabilizer aterpolymer composed of:

    ______________________________________                                        Ingredients           Mole %                                                  ______________________________________                                        2-acrylamido-2-methylpropane-                                                                       52.0                                                    sulfonic acid, sodium salt (AMPS)                                             acrylamide            32.0                                                    N--methyl-N--vinyl acetamide                                                                        16.0                                                    ______________________________________                                    

This terpolymer, while proving to be effective as a high temperaturefluid loss additive for oil well drilling fluids, has the disadvantageof using in its composition 16.0 mole % of N-methyl-N-vinyl acetamide.This renders the material expensive to use.

If it were possible to use a polymeric high temperature fluid lossadditive and rheology stabilizer that was resistant to highcalcium-containing brines, an improvement in the art would be afforded.

THE INVENTION

The invention comprises the utilization of terpolymers with thefollowing composition:

    ______________________________________                                                           Mole %                                                     Ingredients          Preferred                                                                              General                                         ______________________________________                                        2-acrylamido-2-methylpropane-                                                                      58.4     57-61                                           sulfonic acid, sodium salt (AMPS)                                             acrylamide           32.5     20-35                                           N,N--diallylacetamide                                                                              09.1      4-23                                           ______________________________________                                    

As will be shown hereafter, these terpolymers provide excellent hightemperature fluid loss protection to a clay-based brine prepareddrilling fluid.

These terpolymers may be prepared in accordance with the followingpreparative technique, illustrating the preparation of the preferredterpolymer listed above:

A polymerization vessel fitted with a stirrer, thermometer, condenserand addition funnel was charged with 150 g of water and 8.3 g ofN,N-diallylacetamide. The solution was purged with nitrogen for 25minutes while the temperature was raised to 80° C. In a separate vessel,a monomer solution was prepared consisting of 260 g of water, 79.5 g of2-acrylamido-2-methyl-propanesulfonic acid, 31.5 g of a 50% solution ofsodium hydroxide, and 33 g of a 46% solution of acrylamide. This monomermixture was adjusted to a pH of 8.67 and charged to the addition funnel.The solution of monomers was added continuously over a four-hour periodwith four portions of 0.05 g of ammonium persulfate added at 45 minuteintervals beginning at the first addition of monomers. After theaddition of monomers was complete, the reaction temperature wasmaintained at 85° C. for about 90 minutes. The final polymer solutionhad a Brookfield viscosity of 325 cps.

The amount of polymer used to stabilize clay-based drilling fluids underconditions of high temperature and pressure may vary between 10% up to60% by weight based on the clay present in the fluid.

The polymers may be further characterized as having a molecular weightbelow 1,000,000. Preferably, they have a molecular weight within therange of 10,000-500,000.

To illustrate the invention, the preferred composition shown above wastested in a high temperature, high pressure fluid loss additive testwhich is described in detail in the American Petroleum Institutepublication, RP13B.

The particular drilling fluid tested contained 15 pounds/barrel of apre-hydrated Bentonite drilling fluid clay and a 50% dilution of a brineknown as a Williston Basin brine. This brine contained a substantialamount of calcium.

The blank test produced a filtrate of 42 ml/7.5 min.

The preferred composition of the invention was added to provide 6pounds/barrel of active polymer. This provided an approximate dosage of40% by weight active polymer based on active clay. At the end of 30minutes, the fluid loss in the above described test was 15 ml.

Using the same preparative technique and test method for determiningfluid loss additive effectiveness, the following additional polymerswere prepared and tested;

    ______________________________________                                         AMPS    Acrylamide                                                                              ##STR1##         Fluid LossHTHP                            ______________________________________                                        58.5    32.4      9.1              17 ml.                                     60.7    34.9      4.4              17 ml.                                     57.0    20.4      22.6             18 ml.                                     ______________________________________                                    

We claim:
 1. Novel water-soluble terpolymers having a molecular weightbelow 1,000,000 comprising:

    ______________________________________                                        Ingredients           Mole %                                                  ______________________________________                                        2-acrylamido-2-methylpropane-                                                                       57-61                                                   sulfonic acid, sodium salt (AMPS)                                             acrylamide            20-35                                                   N,N--diallylacetamide  4-23                                                   ______________________________________                                    


2. A novel water-soluble terpolymer comprising:

    ______________________________________                                        Ingredients           Mole %                                                  ______________________________________                                        2-acrylamido-2-methylpropane-                                                                       58.4                                                    sulfonic acid, sodium salt (AMPS)                                             acrylamide            32.5                                                    N,N--diallylacetamide 09.1                                                    ______________________________________                                    


3. The novel water-soluble terpolymers of claim 1 wherein saidterpolymers have a molecular weight within the range of 10,000-500,000.